This invention relates to disk drive data storage devices, and more particularly to the manufacture of substrates used in disk drive data storage devices.
Disk drives for computers store data on magnetic recording disks, each including a substrate surface formed of glass, ceramic, glass-ceramic or oxidized metal. Transducer heads driven in a path toward and away from the drive axis write data to the disks and read data from the disks. During manufacture of the disks, the surfaces upon which data will be stored are ground and polished to provide a smooth surface. After cleaning the surfaces, the substrates are sputtered with a series of layers, for example a chrome underlayer, a magnetic layer and a carbon protection layer. The sputtered layers replicate the substrate surface morphology, creating either a smooth or a rough surface on the finished disk. A smoother surface topography on the substrate allows the head to fly closer to the disk, which produces a higher density recording. Glide height for some computer disk drive files is on the order of 20 nanometers (about 200 xc3x85) and less, which is an extremely small interface distance.
In use, when the transducer head of the disk drive glides over the surface, it may crash into asperities in a rough or otherwise smooth surface that are higher than the glide clearance. This is known as a glide defect, which can ultimately cause file failure. A fatal head-disk crash may result in the loss of all data stored on the disk drive. Thus, there is a need to provide an asperity-free surface on magnetic recording disks to avoid head-to-disk crashes and thermal asperities which cause magnetic erasures.
In addition, to be competitive in the disk drive business, a reduction in cost per megabyte is needed, which is highly dependent upon an increase in aerial density. To increase the density requires lowering the fly height, or glide height, of the head. As the head-disk spacing is reduced and aerial density is increased, the magnetic recording disk generally needs an asperity-free/scratch-free surface to keep glide errors or head crash levels the same or lower than with previous disks, and to maintain or improve soft error rates, i.e., recoverable errors. A smoother surface topography includes lower Rq""s, Rp""s and Rmax, as measured by an atomic force microscope (AFM). Rq refers to the root mean square roughness, which designation of surface roughness is well-known in the art. Rp refers to the average height of the peaks above the average roughness. Rmax refers to the difference between the highest peak and the lowest valley, and is a measure of asperities and scratches.
However, with a very smooth disk, i.e., very low Rq and Rp""s, there is significant flying instability and off-track forces that cannot be corrected by the file track positioning servo and that contribute to soft errors. As head-disk interfaces get smaller, such as around 80 xc3x85 or less, the surface attraction between surfaces increases, creating a pulling force that causes instability during flight of the transducer head. Thus, an asperity-free/homogeneous, smooth surface (low Rmax:Rp) is needed to accommodate low glide heights, yet a texture or roughness (Rq) is needed to avoid forces that create head instability and off-track errors. Current substrate finishing technologies cannot supply these competing needs of both low Rmax:Rp ( less than 1.4) smoothness and high Rq ( greater than 3 xc3x85) roughness on the same disk. Currently, an increase in Rq results in an increase in Rp and Rmax, and Rmax becomes significantly larger than Rp, thereby providing an inhomogeneous surface. When the surface is inhomogeneous, magnetic defects from thermal asperities and/or head-to-disk crashes occur.
It is thus desired to provide a method of manufacturing a substrate surface for a magnetic recording disk such that the Rq can be controlled independently from the Rp""s and Rmax, and such that a substrate surface topography is provided having both a smooth and homogenous AFM peak distribution (low Rp and Rmax:Rp) of low enough values to allow low fly height without thermal asperities or head crashes, and a Rq of sufficient value to prevent forces that cause head flying instability and off-track errors, both of which increase the number of soft errors.
The invention addresses these and other problems associated with the prior art by providing a method for texturing magnetic disk substrates in which substrates are produced having an isotropic or anisotropic textured surface topography including a Rp value of about 20-200 xc3x85 and a ratio of Rmax:Rp of about 1.4 or less. In an exemplary embodiment, a glass substrate is produced having colloidal silica particles on a surface thereof at a density of at least about 25 particles per 25 xcexcm2, wherein the textured surface topography includes a Rp value of about 20-200 xc3x85, a micro-roughness Rq of about 10 xc3x85 or less, and a ratio of Rmax:Rp of about 1.4 or less. An exemplary method of the invention includes first providing a smooth, isotropic substrate surface having a surface micro-roughness Rq of about 4 xc3x85 or less, and advantageously a micro-roughness Rq of about 2 xc3x85 or less, a Rp value less than about 20 xc3x85, and a Rmax less than about 30 xc3x85, and then depositing colloidal particles on the surface to alter the surface topography thereby providing a Rp value of about 20-200 xc3x85 and a ratio of Rmax:Rp of about 1.4 or less. In a further exemplary embodiment, the method increases the micro-roughness Rq, but to a value that is still less than about 10 xc3x85. Another exemplary method of the invention includes first providing a textured, anisotropic substrate surface having a surface micro-roughness Rq of about 10 xc3x85 or less, and advantageously a micro-roughness Rq of about 7 xc3x85 or less, a Rp value less than about 30 xc3x85, and a Rmax less than about 85 xc3x85, and then depositing colloidal particles on the surface to alter the surface topography thereby providing a Rp value of about 20-200 xc3x85 and a ratio of Rmax:Rp of about 1.4 or less.
These and other advantages and features, which characterize the invention, are set forth in the claims annexed hereto and forming a further part hereof. However, for a better understanding of the invention, and of the advantages and objectives attained through its use, reference should be made to the accompanying Detailed Description, in which there is described exemplary embodiments of the invention.